Immune dysfunction, susceptibility to sepsis and multiple organ failure are complications associated with thermal injury. Evidence suggests that activation of a pro-inflammatory cascade after burn injury plays an important role in their development. With regards to this, macrophages (Mphi) are major producers of pro-inflammatory mediators with increased productive capacity being observed post-burn. Thus, Mphi hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) may be of fundamental importance in the development of these complications. Nonetheless, the precise mechanisms responsible for the alterations in Mphi activity are unclear. We have utilized a murine scald burn model (3rd degree, 25 percent total body surface area) and our preliminary results indicated that at 4-7 days post-burn Mphi were "hyperactive" as increased productive capacity for nitric oxide, TNF-alpha, IL-6 and PGE2 was observed. Furthermore, at 4-7 days post-burn, but not earlier, Mphi hyperactivity was responsible for the suppression of T cell function and at 7 days post-burn mice were significantly more susceptible to the lethal effects of sepsis. With regards to T cells, we have observed significant mortality (approximately 75 percent) during the initial 48 hr. post-burn period in mice lacking gamma/delta T cells (gamma/delta T cell knock-out mice) and Mphi isolated from surviving mice at 7 days post-burn appear not to be "hyperactive". These findings suggest a dual role for gamma/delta T cells in burn injury pathogenesis; 1) survival early and; 2) induction of Mphi hyperactivity later. Our preliminary results suggest that Mphi hyperactivity post-burn is related to alterations in sensitivity to CAMP, however, the mediators and mechanisms responsible for Mphi hyperactivity post-burn and its role in immune dysfunction remain to elucidated. Moreover, the impact of burn excision, a common clinical practice, on Mphi hyperactivity and susceptibility to sepsis post-burn is unknown. It is our hypothesis that Mphi hyperactivity post-burn is mediated by gamma/delta T cells and altered cAMP responses leading to the development of immune dysfunction. Therefore, we propose to determine the following: 1) The relationship between gamma/delta T cells, Mphi and survival early (initial 48 hr.) post-burn; 2) The role of gamma/delta T cells in the induction of Mphi hyperactivity late (7 days) post-burn; 3) The mechanisms responsible for Mphi hyperactivity post-burn; and 4) The effect of burn wound excision on Mphi hyperactivity and increased susceptibility to sepsis. A more comprehensive understanding of the relationship between Mphi activity, T cell function, and the development of immune dysfunction following thermal injury should hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.